Evaluating the expression of estrogen receptor (ER) is a standard practice for breast carcinoma since it harbors both prognostic and predictive value.1, 2, 3 ER status should be determined on all primary and recurrent breast carcinomas based on the American Society of Clinical Oncologists (ASCO)/College of American Pathologists (CAP) guidelines.4 The gene discussed is ESR1; the disease is breast carcinoma.